Constant frequency oscillation generator



June 13, 1939. J. N. WHITAKER CONSTANT FREQUENCY QSCILLATION GENERATORFiled Jan. 5. 1938 m u h u l u fi fi III-II bill-I r @w x K mw Q u Q EmTl km i 4 u .m RJM Q l u u v .itil u u *6? n u w .n PM: (a h 1. mw 11Lmm INVENTOR. #624 5.5 N. WHITAKER ATTORNEY.

Patented June 13, 1939 UNITED STATES CONSTANT FREQUENCY OSCILLATIONGENERATOR James N. Whitaker, Tuckahoe, N. Y., assignor to RadioCorporation of America, a corporation of Delaware Application January 5,

2 Claims.

This invention relates to vacuum tube oscillation generators, and hasfor its primary object to provide an oscillation generator which canproduce oscillations of constant audible fre- 5 quency and constantamplitude. Further objects are: To provide such a generator which issubstantially free from the generation of harmonic frequencies; toproduce oscillations which are substantially constant regardless of theusual fluctuations in power supply voltages within a range of plus andminus to produce oscillations which are substantially constant withchanges in ambient temperature in a range between 50 and 100 F.; and toprovide a simple, accurate and economical tone source of almost anydesired audible frequency.

The foregoing objects are, in general, achieved in accordance with thepresent invention by the provision of a pair of cascaded amplifiertubes, one of said amplifiers serving the dual purpose of limiting theamplitude and reversing the phase of the energy fed back to the otheramplifier. A stabilizing resistanceis provided in the feedback pathbetween the output circuit of the limiter tube and the resonant inputcircuit of the other tube of the pair for preventing changes in thevacuum tube circuit constants from aifecting the resonant circuit.

One advantage of the present invention is that the limiter and phaseinverter amplifier tube improves the stability of the frequency andamplitude of the system, while at the same time simplifies theconstruction of the resonant circuit.

Other objects, advantages and features will appear from a reading of thefollowing description, which is accompanied by a drawing wherein thesingle figure illustrates a complete oscillation generation system inaccordance with the invention, including a power supply system.

Referring to the drawing, there is shown a multi-vacuum tube toneoscillation generator comprising a pair of amplifier tubes TI and T2.Although TI is here shown as two tubes, it will of course be obviousthat it may be a twin-triode tube having two space discharge paths. Fromone of the anodes of TI feed-back energy is supplied to theamplitude-limiter driving tube T2 and from the other anode M of TIoutput energy is supplied through a suitable transformer 24 to autilization circuit 25.

A conventional type of power supply system 26, employing a suitabletransformer 33, a full wave rectifier 34, a pair of voltage regulatortubes 3|, 32, and a resistor-capacitor filter 21, serves 1938, SerialNo. 183,401 (oi. 25036) to pass operating potentials to the variousportions of the oscillation circuit.

Tl comprises, in effect, two Class A amplifiers for producing linearamplification of the energy impressed on grids l2 and [3. The usualcathode 5 resistor and condenser combination III, II provides theautomatic bias for the grids l2 and |3. Coupled to the grid l2 andcathode I6 is a tuned oscillatory circuit comprising an iron-coreinductance I having in shunt therewith a main 10 tuning condenser 2. Avariable resistor 4, in series with a Vernier condenser 3, both in shuntto the tuned circuit I, 2, serves to change the frequency ofoscillations produced in the generator. The anode l5 of one of the spacepaths 15 of amplifier TI is connected through a blocking condenserl8 tothe grid 28 of the amplitude limiter drive tube T2. A suitablepotentiometer 9 in the grid circuits of the twin-space path amplifier TIis used to vary the alternating cur- 20 rent potential applied to gridl3 through its movable member 29', thus governing the level of theenergy supplied to the transformer 24. Potentiometer 9 also serves toprovide a leakage path to ground for grid l2 and L3.

The feed-back of energy from the anode or output electrode 2| of tube T2to the grid input electrode l2 of one space path of TI over path 29 isinsuch phase and of such magnitude as to overcome the losses in thecircuit and produce 30 oscillations. Putting it another way, it may besaid that the voltage gain of the tubes TI and T2 is unity or greaterbetween grid l2 of tube TI and the anode 2| of tube T2.

serially connected in the feed-back path 29 is 35 a coupling condenser 6and a stabilizing resistor 5. Resistor 5 is relatively high comparedwith the anode resistance of tube T2, and makes the resistance which thetuned circuit i, 2 sees when looking toward the anode 2| substantiallyin- 40 dependent of the electrode voltages. We thus have a resistancestabilized oscillation. generator.

Tube T2 is biased to function as an overloaded drive tube, thus limitingthe amplitude of the energy fed back over path 29. connected to groundthrough resistor I9, and the energy supplied to this grid from the anodel5 of tube TI is sufficient to cause the anode current in tube T2 torise to a point of saturation on the positive half of the cycle, and todrop to 50 zero on the negative half of the cycle, thereby producing theeffect of amplitude limiting.

Suitable positive potentials are supplied from the power supply system26 to the anodes l4 and I5 of the twin space path amplifier Tl throughthe 55 The grid 20 is 45 resistor l1 and the primary winding of audiotransformer 24, respectively, and to the anode 2| of tube T2 throughresistor 23.

The operation of the oscillation generator is as follows: Any voltageappearing across the tuned circuit l, 2 is impressed on the grids l2, l3and cathode N5 of the amplifier Tl, whereupon it develops a voltage onthe anode l5 substantially 180 out of phase with the original voltage.This developed voltage is transmitted to the grid 20 of theamplitude-limiter tube T2 through condenser IB. Tube T2 functions notonly as a limiter but also produces on the anode 2| a voltage which isagain reversed substantially 180 with respect to the voltage on grid 20,but now in phase with the original voltage on grid l2. It will thus beseen that the tube T2 functions both as a limiter and as a phaseinverter.

It has been found that the combination of a resistance-stabilizedoscillator with the amplitude and phase reversing tube in the feed-backcircuit has produced an oscillation generator of remarkable constancy offrequency and output, and one which is simple and economical toconstruct.

In .one embodiment used in practice, the elements contained within thedotted box 28, consisting of resonant circuit I, 2, Vernier adjustmentelements 3, 4, stabilizing resistor 5, and coupling condenser 6, werebuilt up in an assembly separate and apart from the tube circuit per se.Plugs were used on this assembly while cooperating jacks were employedin the tube circuit for connecting the elements together. With thisembodiment, the frequency remained constant within .012%, while theoutput level remained absolutely constant, so far as could be observedwith the measuring instruments employed.

It will be appreciated, of course, that anyone skilled in the art canmake various modifications in the circuit of the invention withoutdeparting from the spirit and scope of the appended claims. For example,certain resistors such as I1 and 23 can be replaced by suitableinductance coils; resistor 4 and Vernier 3 can be omitted; whileinductance I can be made to be variable, etc.

What is claimed is:

1. A constant frequency, constant amplitude oscillation generationsystem comprising two sets of linear amplifier elements each having aninput and an output circuit, a frequency controlling circuit connectedto the input circuits of both sets of linear amplifier elements, afeed-back circuit from the output circuit of one set of amplifierelements to said frequency controlling circuit, said feed-back circuitincluding an electron discharge device whose grid is biased to givesaturated output current upon the application of a slight positivepotential to said device from said last set of amplifier elements, saiddevice having input potentials applied to its grid from said last outputcircuit and having its anode coupled to said frequency determiningcircuit through a stabilizing resistance, whereby the phase of theenergy in the anode circuit is reversed relative to the energy in thegrid circuit, a utilization circuit coupled to the output circuit ofsaid other set of amplifier elements, and a potentiometer in the inputcircuit of said last set of amplifier elements for regulating the levelof the energy supplied to said utilization circuit.

2. A constant frequency, constant amplitude oscillation generationsystem comprising two sets of linear Class A amplifier elements eachhaving an input and an output circuit, a parallel tuned frequencycontrolling circuit comprising inductance and parallel capacitanceconnected to the input circuits of both sets of linear amplifierelements, a feed-back circuit from the output circuit of one set ofamplifier elements to said frequency controlling circuit, said feed-backcircuit including an electron discharge device whose grid is biased togive saturated output current upon the application of a slight positivepotential to said device from said last set of amplifier elements, saiddevice having input potentials applied to its grid from said last outputcircuit and having its anode coupled to said frequency determiningcircuit through a stabilizing resistance, whereby the phase of theenergy in the anode circuit is reversed relative to the energy in thegrid circuit, said resistance being high compared to the anoderesistance of said electron discharge device, a utilization circuitcoupled to the output circuit of said other set of amplifier elements,and a potentiometer in the input circuit of said last set of amplifierelements for regulating the level of the energy supplied to saidutilization circuit.

JAMES N. WHITAKER.

